Reactive ion etching (RIE) can be used for etching silicon carbide (SiC) to obtain a desired microstructure. For example, batch fabricated pressure sensors in SiC wafers using conventional RIE or its variations (e.g., inductively coupled plasma deep reactive ion etching (ICP-DRIE)) have become the standard for fabricating structures in SiC. For instance, to produce SiC pressure sensors for low pressure applications of less than 20 psi, the diaphragm of the sensors must be thinned down to thicknesses of less than 10 microns. The utilization of RIE or ICP-DRIE to accomplish this has been unsuccessful, largely due to the introduction of etch-induced defects that compromise the structural integrity of the thin diaphragm, i.e., the reliability of the sensor. This may also cause a significant drop in the full scale output of the sensor, thereby constricting the application or use of the sensor.
A significant adverse effect of an etch-trench artifact is that it prevents the diaphragm from being thinned down in order to increase the sensitivity and resolution of the sensor and prevents the sensor from being used in very low pressure environments. Current technology limits the diaphragm thickness to 25 microns and limits the sensor applicability to approximately 50 psi. Below this pressure, the sensor becomes less sensitive and signal-to-noise ratio degrades significantly.
The inability to produce thinner diaphragms to allow for lower pressure sensing effectively precludes the use of SiC pressure sensors for sub-psi dynamic pressure sensing that is beneficial for combustor dynamics studies. Furthermore, because RIE is a blind, directional, and sometimes non-uniform process, it results in the creation of etch-induced defects that are known to cause reliability problems, such as premature failures. Thus, it may be beneficial to provide a method of fabricating thinner microstructures in SiC.